This invention relates to copolymers, more particularly to polyesters of the polyesters with phosphorus containing compounds, which have enhanced heat stability.
Many applications of engineering plastics require polymers that have long term heat stability along with other properties such as tensile strength and chemical resistance. Conventional commercial polyesters generally have good long term heat stability, and possess other desired property attributes such as excellent mechanical properties, good surface finishes of molded articles and satisfactory chemical resistance. It has been shown however than halogen-free flame retardant polyester formulations based on organic P-compounds have often no good long term heat stability properties.
Several attempts have been made to prepare halogen-free flame retardant polyester formulations. It has been known in the past the process to make polyesters flame retardant by using halogen-free flame retardants based on P-containing and N-containing compounds. The JP06157880 describes filled polyesters containing melamine cyanurate and an aromatic phosphate and JP3115195 polyester with N-heterocyclic compounds and a polyfunctional group compound and optionally a P-based flame retardant. The U.S. Pat. No. 4,203,888 teaches polyester with organic diphosphates. However the polyester compositions possess no good thermal stability especially on prolonged heat aging. There is a need for polyesters having improved long term heat aging characteristics.
There is a continuing need to provide a novel halogen-free flame retardant polyester material having improved long term heat resistance, processability, mechanical strength and moldability properties.